CONTRACTILE PROPERTIES AND FIBER-TYPE DISTRIBUTION OF QUADRICEPS MUSCLES IN ADULTS WITH CHILDHOOD-ONSET GROWTH-HORMONE DEFICIENCY

Adults with GH deficiency (GHD) report weakness and fatigability. The origin of such symptoms is still debated. This work aimed to clarify w hether weakness and fatigability depend on impairment of skeletal musc le contractile capacity. Five males with childhood-onset GHD (age +/- SE, 29.6 +/- 1.9) and 13 age- and sex-matched controls were enrolled i n the study. Quadriceps muscle cross-sectional area (CSA), strength, t witch characteristics, and fatigue index of voluntary and electrically evoked contractions were determined in vivo in all subjects. Fiber ty pe distribution and CSA of identified types of skeletal fibers were de termined on needle biopsy samples of the vastus lateralis muscle of al l subjects. Fiber type distribution was assessed on the basis of myosi n heavy chain (MHC) isoform composition determined by electrophoresis on polyacrylamide gels. Fiber CSA was determined on cross-cryosections of fiber bundles immunostained by monoclonal antibodies against MHC i soforms. Absolute values of strength and fiber CSA of quadriceps were significantly lower in patients affected by GHD than in controls. Howe ver, once strength and fiber CSA were normalized for quadriceps CSA an d subject height, respectively, differences disappeared. No difference was found between GHD patients and controls for quadriceps muscle twi tch characteristics, fatigue index, and fiber type distribution. The r esults reported here suggest that weakness and fatigability in childho od-onset GHD do not have a skeletal muscle origin.